Signal receiving system



Filed April 2'1, 195s MOPQNPND Patented Mar. 1 19, 1940 PATENT OFFICE 2,193,801 SIGNAL RECEIVING, SYSTEM John F. Byrne, Cedar Rapids, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a

corporation of Iowa Application April 21, 1938, Serial No. 203,436

4 Claims.

My invention relates broadly to suppressed carrier signalling systems and more particularly to a receiving system for suppressed carrier transmission embodying a novel method of pro- 6 viding for restoration of the carrier for demodulation of the signal.

Oneof the objects of'my invention is to provide a suppressed carrier receiving system, having a local oscillator producing a wave of car l rier frequency, with means forcontrolling the frequency of the oscillator directly from the received signal.

Another object of. my invention is to provide a method of restoring the carrier in a suppressed u carrier signal wave by mixing the received wave and a locally generated wave controlled in frequency by selected components in the received Wave. s

yA further object of my invention is to pro- 20 vide a receiving system for suppressed carrier transmission which operates efliciently and produces a signal of improved clarity due to direct I 25, A still furtherobject of my invention is to provide a suppressed carrier receiving system having a dual channel portion one side of which includes a selective circuit for deriving high frequency components from the received Wave, an 30 oscillator controlled in frequency by the selected components, and a phase correcting network, the output of thisl channel being mixed with the full signal complement inthe output of the other channel for restoring the suppressed carrier for 35 subsequent demodulation of the signal.

Other and further objects ofl my invention reside in the system as hereinafter more fully set forth, with reference to the accompanying drawing which shows in diagrammatic form the essen- 40 tial features of my invention My invention concerns a method of dernodulation which when used to demodulate suppressed carrier transmission results in an audio frequency signal ofl high quality. Inrany double side band suppressed' carrier system, when the carrier is reintroduced at the receiver, extreme care must be taken in order to insure that the reintroduced carrier is in phase with, or 180 degrees out of phase with the initial carrier. If this condition is not maintained, serious distortion of the signal Wave occurs vin all types of demodulators. My invention particularly deals with a method of obtaining and maintaining the correct4 carrier 55 phase for reintroduction and demodulation.

namely, the carrier, the upper side band and the lower side band. The side band frequencies are displaced equal amounts from the carrier frequency, and in suppressed carrier transmission they are located at points in the frequency spectrum that are equally above and below the original carrier frequency. For example: Suppose that a 100,000 cycle carrier is modulated yby a l1'0- 2,000 cycle source, Y,The frequencies present are v 100,000-2,000, 100,000, and 100,000+2,000. These are respectively, the lower side band, the carrier and the upper side band. In a suppressed carrier system the frequencies would be 100,000-2,000 and l00000-{-2,000 cycles.

The demodulaticn arrangement forv suppressed carrier reception in the system of my invention provides for the passage of the side band frequencies into a detector. It islrnown that in the output of such a device, when two frequencies, A and B, are impressed on the input, the following frequencies appear:

A, which is the lower side band 100,0002,000, or 25 B, which is the upper'side band 100,000+2,000, 0r

A+B,jwh1ch is 200,000;

A-B, Which is 4,000; 30

2A, which is 200,000-4,000, or 196,000;

2B, which is 200,000+4,000, or 204,000.

Of particular interest is" the frequency A-l-B- Whichis equal to twice the original carrier frequency;v The load in the plate circuit of the detector is resonated at twice carrier frequency, the principal voltage occurring across the system being at exactly twice the frequency of the original carrier. It should be noted that this is true system. The suppressed carrier transmission is 55 received in the antenna, consisting of frequencies p f 't2-1r and and amplified in the high frequency amplifier at I. Part of the amplified output is utilized for detection in the detector 2, the output circuit of which includes resonant circuit 8 tuned to 2f, twice the carrier frequency. This output of the detector is utilized to control the frequency of an oscillator 3 at the frequency f of the carrier, and a phase shifting network is provided at 4 to adjust the phase of the current fed into the mixer 6 to its proper relation in respect to the carrier components in the received wave.

The remainder of the output of the amplifier I is passed into the amplifier` ii and thence directly to the mixer The function of the mixer is to reconstruct an amplitude modulated wave, the side band frequencies being obtained from the output of amplier 5, and the carrier at proper phase from the output of the ph ase shifter 4. After mixing. a conventional demodulator l of the type used for amplitude modulated waves, is utilized to convert the high frequency input into low frequency (audio) Signals.

I have described my invention in its essential elements and the combination thereof in a preferred arrangement in accordance with my invention. I desire it to be understood that various modifications may be made in the basic arrangement illustrated and any suitable apparatus may be employed in the respective units. I intend no limitations upon my invention except as are imposed by the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is as follows:

l. The method of restoring the carrier in a suppressed carrier signal wave for demodulation which comprises producing a local oscillation at the frequency of the carrier wave, deriving components of twice the carrier frequency from thc received wave, controlling the frequency of the local oscillation by said components of twice the carrier frequency, and mixing the local oscillat'ion and the received wave for reconstructing the original amplitude modulated wave.

2. In a system for receiving a double side band suppressed carrier transmission, means for deriving a controlling wave at twice carrier frcquency from the sum of the side band waves, a local oscillator having a connection from said means for control by the said controlling wave and operative to deliver an oscillation at carrier frequency, means coupled with said oscillator for adjusting the phase of said oscillation in synchronization with the suppressed carrier transmission, and means for combining said oscillation and the double side band transmission for reconstructing the original amplitude modulated wave.

3. In a system for receiving a double side band suppressed carrier transmission, a detector circuit supplied with the double side band transmission for producing a component of twice carrier frequency, an oscillator operative to deliver an oscillation at the carrier frequency, and means interconnecting said detector circuit and said cscillator for utilizing the component of twice carrier frequency for controlling the frequency of the oscillator at carrier frequency for combination with the double side bands to reconstruct the original amplitude modulated wave.

4.. In a system for receiving a double side band suppressed carrier transmission, an oscillator, means having a connection to said oscillator and supplied with a portion of the suppressed carrier transmission for obtaining by coaction of the side band' frequencies a controlling wave for controlling the frequency of the oscillator, said oscillator being operative to provide a current at carrier frequency, and means supplied with said current at carrier frequency and said double side band transmission for reconstructing the original amplitude modulated wave for purposes of demodulation.

JOHN F. BYRNE. 

